Bucking Carol, Wood Chris M
McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada, L8S 4K1.
J Exp Biol. 2008 Aug;211(Pt 15):2533-41. doi: 10.1242/jeb.015610.
We investigated the potential acid-base and nitrogenous waste excretion challenges created by voluntary feeding in freshwater rainbow trout, with particular focus on the possible occurrence of an alkaline tide (a metabolic alkalosis created by gastric HCl secretion during digestion). Plasma metabolites (glucose, urea and ammonia) were measured at various time points before and after voluntary feeding to satiation (approximately 5% body mass meal of dry commercial pellets), as was the net flux of ammonia and titratable alkalinity to the water from unfed and fed fish. Arterial blood, sampled by indwelling catheter, was examined for post-prandial effects on pH, plasma bicarbonate and plasma CO2 tension. There was no significant change in plasma glucose or urea concentrations following feeding, whereas plasma ammonia transiently increased, peaking at threefold above resting values at 12 h after the meal and remaining elevated for 24 h. The increased plasma ammonia was correlated with an increase in net ammonia excretion to the water, with fed fish significantly elevating their net ammonia excretion two- to threefold between 12 and 48 h post feeding. These parameters did not change in unfed control fish. Fed fish likewise increased the net titratable base flux to the water by approximately threefold, which resulted in a transition from a small net acid flux seen in unfed fish to a large net base flux in fed fish. Over 48 h, this resulted in a net excretion of 13 867 micromol kg(-1) more base to the external water than in unfed fish. The arterial blood exhibited a corresponding rise in pH (between 6 and 12 h) and plasma bicarbonate (between 3 and 12 h) following feeding; however, no respiratory compensation was observed, as PaCO2 remained constant. Overall, there was evidence of numerous challenges created by feeding in a freshwater teleost fish, including the occurrence of an alkaline tide, and its compensation by excretion of base to the external water. The possible influence of feeding ecology and environmental salinity on these challenges, as well as discrepancies in the literature, are discussed.
我们研究了淡水虹鳟鱼自愿摄食所带来的潜在酸碱和含氮废物排泄挑战，特别关注碱性潮（消化过程中胃分泌盐酸导致的代谢性碱中毒）可能出现的情况。在自愿摄食至饱足（约占体重5%的干商业颗粒饲料）前后的不同时间点，测量了血浆代谢物（葡萄糖、尿素和氨），以及未喂食和喂食鱼向水中的氨净通量和可滴定碱度。通过留置导管采集动脉血，检测餐后对pH值、血浆碳酸氢盐和血浆二氧化碳张力的影响。摄食后血浆葡萄糖或尿素浓度没有显著变化，而血浆氨短暂升高，在餐后12小时达到静息值的三倍峰值，并在24小时内保持升高。血浆氨的增加与向水中的氨净排泄增加相关，喂食鱼在摄食后12至48小时内将其氨净排泄量显著提高了两到三倍。这些参数在未喂食的对照鱼中没有变化。喂食鱼同样将向水中的可滴定碱净通量增加了约三倍，这导致从未喂食鱼中观察到的少量净酸通量转变为喂食鱼中的大量净碱通量。在48小时内，这导致向外部水中排泄的碱比未喂食鱼多13867微摩尔·千克⁻¹。喂食后动脉血的pH值（在6至12小时之间）和血浆碳酸氢盐（在3至12小时之间）相应升高；然而，未观察到呼吸代偿，因为动脉血二氧化碳分压保持不变。总体而言，有证据表明淡水硬骨鱼摄食会带来诸多挑战，包括碱性潮的出现，以及通过向外部水中排泄碱来进行代偿。文中讨论了摄食生态和环境盐度对这些挑战的可能影响，以及文献中的差异。
